Stabilized control system



April 29, 1952 H. zn-:BOLz Er A1.

STABILIZED CONTROL SYSTEM 3 Sheets-Sheet l Filed May 18, 1946 April 29, 1952 H. zlEBoLz r A1.

STABILIZED CONTROL SYSTEM 3 Sheets-Sheet 2 Filed May 18, 1946 NN bm] April 29, 1952 H. ZIEBoLz Er A1.

STABILIZED CONTROL SYSTEM 3 Sheets-Sheet 5 Filed May 18, 1946 Patented pr. 29, 1952 STABILIZED CONTROL SYSTEM Herbert Ziebolz and signors to Askania Re cago, Ill., a corporation Paul Glass, Chicago, Ill., asgulator Company, Chiof Illinois Application May 18, 1946, Serial No. 670,679

(Cl. S18-28) 15 Claims.

The invention relates generally to control systems and more particularly to a system for controlling a variable, such as pressure, temperature, rate of `fiow or the like.

One object of the invention is to provide a new and improved system for the control of a variable which system is unusually rapid yet very stable in operation.

'Another object is to provide a new and improved control system in which the adjustment given a controlling member upon departure of the variable from a predetermined value is approximately proportional to the departure of the variable and is made at a progressively slower rate as the controlling member approaches the end of any particular adjustment.

Still another object is to provide a control system for a variable having proportional con-` trol means driven through a planetary gear system from the means controlling the variable, and from means, brought into operation as a result of adjustment of the controlling means, tending to restore the proportional control means at an exponential rate.

Yet another object is to provide a control system of the character immediately above defined in which the means tending to restore the proportional control means at an exponential rate is adjustable to vary its rate of operation.

A further object is to provide a system for controlling a variable having means for controlling the variable, means coming into play asan incident to adjustment of the controlling means and tending to counteract the called-for adjustment of the controlling means, and means also brought into operation as an incident to adjustment of the controlling means functioning to `determine the effectiveness of the counteracting, means, both of said last named means tending to be restored to a normal position by asymptotic means.

Yet a further object is to provide a control system for controlling a variable having means for controlling the variable, means coming into play as an incident to adjustment of the controlling means tending to counteract the calledfor adjustment of the controlling means, and means also coming into play as an incident to adjustment of the controlling means in turn determining the effectiveness of the counteracting means, both of said last mentioned means being influenced at the same rate by adjustment of the controlling means but infiuenced to return to normal position by means operating on the same rate pattern but possibly at different specific rates.

Still a further object is to provide a system for controlling a variable having means for controlling the variable, means coming into operation as an incident to adjustment of the controlling means to tend to counteract the calledfor adjustment of the controlling means, and means also coming into play as an incident to adjustment of the controlling means operable to govern the eiectiveness of the counteracting means, the last mentioned means being permissibly adjustable not only to delay or reduce the effect of the counteracting means, but also to aid the called-for adjustment of the controlling means.

Other objects and advantages will become apparent from the following detailed description taken in connection withA the accompanying drawings, in which:

Fig. 1 is a diagrammatic illustration of a stabilized control system embodying the features of this invention.

Fig. 2 is a diagrammatic illustration of a slightly modified form of the system disclosed in Fig. 1. y

Fig. 3 is a diagrammatic illustration of still another' modified form of the system shown in Fig. l.

While the invention is susceptible of numerous modifications and alternative constructions, it is herein shown and will hereinafter be described in three embodiments. It is not intended, however, that the invention is to be limited thereby to the specific disclosures made. On the contrary, it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as defined in the appended claims.

' Generally speaking, the system disclosed herein in the several embodiments is adapted and intended for the control of' any variable subject to control such, for example, as pressure. temperature, flow, etc. Usually it is the purpose of a control system to maintain the variable constant at some predetermined value and the invention herein is designed to serve that end though it might be employed to serve 'other` control functions. The system comprises means for controlling the variable, and power means for so regulating the controlling means as to maintain constant the variable being controlled. To that end, the system includes means adjustable to indicate the value at which the variable is to be maintained, means responsive tothe variable for indicating the departure of the variable from the predetermined value, and means responsive to the last named plurality of means being also influenced by an apparatus tending* to restore the counteracting means to its normal position at an exponential rate. While all of the embodiments of the invention hereindisf.v

closed incorporate such a counteracting means, each embodiment either contains additional structure or has the various means connected in a manner such that the counteracting means is capable of functioning, and usually does function, in a somewhat differentl manner in each dffthefembodiments thereby producing results which are'v different and advantageous.

Referring first to the embodiment disclosedy in lfof the drawings, the variable to be' controlledfis, for exemplary purposes, considered to bey pressure of some `iluid flowing in a conduit for regulating the pres- I0. The control means sure is here represented'as a valve II, the source Q'ffluid being assumed to beconnected toV the conduitto 'the right of the valvey IIv and the pressure to'` be maintained constant in that portion'ofthe conduit to 'the left of the valve II.

The valve' II is adaptedto be moved to various positions by power means, herein representedv generally, as a motor I2, 'acting' through a shaft I3, bevel I6. The driving means'for the vvalve II must, of course, be capable of actuating'the same in either 'direction andl to varying degrees. Though this might be accomplished With aconstant speed motor and a variable transmission, it is, for simplicity and efficiency, herein accomplished by having the motor I2 la reversible, variable speed motor'.

erein the motor I2 is under thel control o f, three signal generating means I1, I8 and I9. Ofthese, the first signal generating means Il is shown, diagrammatically and is of a character capable of producing a signal corresponding to the predetermined: value atv which thevariable is to bemmaintaned. In other words, this first sigrial ,generatiameens l1 generates. basic Sig-v nal and this means is, moreover, adjustable so,

as to permity of variation of thepredetermined valueat which the variable is to be maintained. The second signal generating means I8 is responsive to the variable and functions when the variable is at the value predetermined by adjustment offtherrst signal generating means l1 to generateda signal which is equal in magnitude but opposite incharacter to they signal generated by the means VI'I in order to counteract and cdmpletely offset that signal. As theY variable departs inV one direction from its predetermined value. specifically, as itri ses above the predetermined value, the signalA generated by the means I8 will exceed thatgenerated by the means I7, and, conversely, if the variable falls below the predetermined value, the signal generated by the means I8,will be smaller than that generated by the meansr I-1. The resultant signal, therefore, willbe ofia magnitude corresponding to the degree of departure of thevariable from the predetermined Value, whilethe character of the signal will cor. respond with the direction of. departure.-

gears I4, a shaft l and bevel gearsA While the signal generating means might generate any one of a variety of signals, they are herein shown as generating electrical signals. The third signal generating means I9, therefore, also is an electrical signal generating means and is shown in greater detail but, nevertheless, by way of example only, as a potentiometer having a winding 2E) connected at Iits endsr to any appropriate source 2I of electrical potential. A movable contact 22 of the potentiometer is by a lead 23 represented as electrically connected to the rst signal generating means Il, while the midpoint of the winding 2d is by a lead 24 connected to afsignal conditioning andA amplifying circuit diagrammatically represented at 25.. The signal generating means I'I and I8 and the circuit 25 are, of course, properly interconnected electrically, such connection being represented diagrammatically by the leads 26 and 21. The signal conditioning and amplifying circuitl 25 maybe of any well known construction` capableof: receiving signals of varying magnitude and op posed character, that is, sign or phase, andof utilizing those signals to cause the motor 'I2fto rotate in one or the other direction, depending upon the character of thev signal, 'and at differ.-r

ent speeds depending upon the magnitudeof the signal. The circuit 25 is diagrammatically shown electrically connected to the motor I2 by the.

lead 23.

As will presentlyy becomeI more` apparent-` the third signal generating'means I9 isconnected in a feed-.back circuit and in this'particularv embodiment is an inverse.feedback functioning toadd stability to thesystem while yet permitting rapid adjustment o-fl the controlling means II to a new position without hunting. 'The signal generati ing means I9 herein'functions to bring about an value, the signal generating means I9 is. so ar# rangedas to counteract or offsetI progressively the signal generated as a result of departure of the variable from its predetermined value asV the valve LI is adjusted. Thesystem is completed by means, generally designated lill'y operating to' remove the eiect ofthe third signalfgenerating means I9, that is, to restore or reset'the meansV I9 to lneutral or normal, so that its signal iwill'. not remain and call for adjustment ofthe valve lI as the variable returns to itspredeterminedV value and the signals of the means Il and I8 again balance o nel another. In order that the third signal generating means I9 maybe actuated firstto vbring aboutY an adjustmentof the valvev proportionatelyto. the variable from its'` predeter-v the departure of y mined.V value by counteracting fthek signal gen1 embed, es

be restored or reset toneutral or normalposi-V tion, itis arranged; to be actuated by the differentialadjustment or actuation of the valve.

means II and the resetting means 30. Tothat end, the fromV a planetary system,f generallyk designated 3I., which in turn has elements thereof driven,

from the valve II and theresetting1 ifneansllg of control mustA Il proportionately to' ther a result of such departure and may then,

signal generating means I9 is driven`- Though disclosed somewhat diagrammatically, the planetary gear system 3I includes a rst driving gear 32 and a second driving gear 33. The gear 32 is fast on the shaft I3 so as to have a direction and extent of rotation corresponding to the direction and extent of adjustment of the valve I I. 'Ihe gear 33 is driven from the resetting means 30, as will presently :be described in greater particularity. Also included is a third element 34 geared infwell known manner to the driving gears 32 and 33 to have a movement representing the differential in the movements of the gears 32 and 33. This third element 34 is through a shaft 35 connected to the movable contact 22 of the signal generating means I9.

The resetting means 39 is of such character that, operating independently, it tends to restore the movable Contact 22 of the signal generating means I9 to its normal or neutral position at a rate decreasing exponentially. This is accomplshed through the employment of means that may be described as asymptotic or asymptotically operating means. This means comprises a iirst disk 31 constantly driven from a constant speed motor 38. A second disk 39 is disposed at right angles to the first disk with its periphery in frictional engagement with a face of the first disk Aand also in frictional engagement with a cylinder 40 fast with the driving gear 33. The disk 39 is mounted for adjustment axially, that is, radially of the disk 31, and it will be appreciated, therefore, that when positioned at the center of the disk 31 it will not transmit any rotation to the cylinder 40 but that, as it is shifted radially outwardly on the disk 31, the rotation transmitted to the roller 43 will increase at an exponential rate. The disk 39 is by a rod 4I and other suitable means, such as a crank 42 if the shaft 35 is rotatable, connected to the shaft 35 so as to partake of the movement given to the shaft by the third element 34 of the planetary gear system 3l. More particularly, the disk 39 is so connected to the shaft 35 that it is positioned axially of the disk 31 when the movable contact 22 of the signal generating means is in its neutral or normal position, and is shifted radially outwardly on the disk 31 as the movable contact 22 is moved away from its neutral or normal position. Shift of the disk 39 with departure of the movable contact 22 from neutral is in all cases radially outwardly but is in diametrically opposite directions with departure of the movable contact to the one or the opposite side of neutral. Thus the direction of rotation of the gear 33 is always proper to tend to restore the contact 22 to neutral posi- Interposed between the constant speed motor 38 and the disk 31 is a variable transmission 43 whereby the speed of rotation of the disk `31 may be altered, and thereby the exponential curve on which the resetting means 3U operates may be altered.

As an aid to full understanding of the invention, the operation thereof will be briefly described. Let it be assumed, therefore, that the variable is temporarily at the value predetermined by adjustment of the first signal generating means I1. Under this condition, the second signal generating means I8 will be generating a signal which exactly balances or offsets the signal of the means I1. The disk 39 will be exactly axially of the disk 31 and thus not transmitting any rotation to the driving gear 33, and the movable contact 22 of the third signal generating means I9 will bein its neutral or normal position so that the signal means I9 willnot be generating any signal. As aconsequence, all of the parts of the system save the disk 31, which is constantly rotated, are at rest and in a normal, neutral or balanced state. Assume next that the supply pressure increases or the load decreases so that there is an increase in the pressure of that portion of the conduit Il] to which the signal generating means I8 is responsive.` Such departure sets up 'a signal callingv for adjustment of the valve II to correct this condition and brings into simultaneous operation various parts of the system. Whilethe various parts or portions of the system, for the most part, operate simultaneously, these operations will, in an attempt tofacilitate, understanding, be herein described as occurring sequentially.

Under the assumptions made and the liberties.

32 also is rotated proportionately to the extentof adjustment of the valve I I, and the element 34 will, therefore, be actuated to in turn move the contact 22 of the signal generating means -I9 away from its neutral position in a direction to cause generation of a signal which is opposed in character to that now being impressed upon the circuit 25. The magnitude of the signal generated by the means I9 increases as the contact 22 is moved away from its neutral position, and thus the signal impressed on the circuit 25 is being reduced progressively as the valve II is being adjusted to a new position. Eventually, the signal generated by the means I9 balances the signal impressed on the circuit 25 by the means I1 and I8, and thus brings the motor to rest even though the means I8 may still be calling for further closing of the valve II because the variable, herein the pressure in the conduit I0, is still above the predetermined value. It will be appreciated that the signal generated by the means I9 has progressively offset, that is,- reduced to zero, the signal difference of the means I1 and I8; and since the speed of operation of the motor I2 is dependent upon the magnitude of the signal impressed on the circuit 25, the rate at which the valve I I is adjusted is progressively reduced as it approaches the end of the adjusting movement, thereby preventing overrunning as an incident to the inertia of the motor I2. l

With the valve II now in a new position restricting the conduit II) to a greater degree, the pressure in the conduit I0 to the left of the valve decreases and with such decrease in pressure the signal generated by the means I8 decreases. It becomes necessary, therefore, to return the movable contact 22 to its neutral position. This is done by the resetting means 30 at rst rapidly, and then progressively more slowly, The means 3i) was rendered operativeby adjustment of the valve II, for as the shaft 35 was actuated by rotation of the gear 32 the disk 39 was shifted radially of the disk 31 with the result that the disk 31 then became operative to rotate the cylinder 40 and the gear 33 fast therewith. Such rotation of the gear- 33,701 .coursecauses movement, ofthe element @tand with itgniovement of the shaft35 and the crank 42. l'lhe resetting v*means 30 is, 'of course, Mso

. assembled thatA .the movement vimparted to the simultaneously. `Withthe first departure of the vaaiablefrom the predetermined value, a signal is Agenerated Vunder fthe-"control ofthe means 'I8 calling for -ladjustment of the valve li. Asthe motor -342 rotates-toleiiect .this adjustment, vit will-simultaneously, through'the planetary gear system, ftend -to vrotate the movable contact 22 of the-means i9 fin aldirection causing generation-cfa signal counter to the signal calling for adjustment of the valve. With the slightest movement'of'themovable contact 22, however, the disk3v9 is shifted andlthus the resetting-means is' rendered loperativefacting L through the plane- .tar-ygear system-to tend to return themovable contact 22 to its neutral position. The .eiect ofthe resetting-meansB Witha small shift of the:disk'39;away'irom'theaxis of the disk'31 is, of course, slight',and fthus lgives the more effective operation oithemotor l2 an opportunity lto `move the contact-l 22 and thus permit it to generate-:a signal halting further adjustment of the=valve H. The precise operation of the system-all dependson the relative speeds at which certain changes occur, that is, the speed at which the Avariable departs from yits predetermined value; `the speed at which it returns to its .predetermined value after adjustment of the valve H; and thespeed -at which the .adjustment of thei-valve tendsto rotate the movable contact 22 in one direction; andthe speed'at which the resetting means 3!! tends to move that contact in the vopposite direction. vThis latter speed, while `:stillbeing exponential, may be varied by adjustment of Athe rate at which the disk 3i rotates.

"Theideal operatioirfoi course, would be 'for thevalve i I to be givena single adjusting movement only, vfith'the variable returned to its-predetermined valueand with the valve in a positiontomaintain that predetermined value just as the movable contaot`22is returned to its neutralposition. This, however, isa practical impossibility for, of' course, to` reduce the pressure in the conduit LiL-fior example, the valve Il must rst be ladjusted-to permit less than that'flow of iluid which would maintain-the-variable Vconstant under-the new conditions. 'This means, of course, that there must be a successiono'ad- 'justments or va continuousfadjustment of the Ishown in`Fig. `2, it will be seen-that ther-system '.is'basicallythej same'- as thatdisclosed in L2Fig.,1,

8 with the .exception `of :the precise effect or" the proportional .control means. v'The invention is still disclosed as embodying :a system for vmaintaining lconstant a variable, herein .the pressure of .the Vduid-in va conduit lil. This pressureiis varied by controlling means taking the form of a valve H' ,drivenin opposite directions .andai varyingspeeds from a reversible, variable speed, electricmotor I2 through ashaft i3 andnecessarygearing or linkage. Governing :the .electric motor-,area rst, a second anda :third electric signal generating means il', i8 and I-S', respectively. 'Of these, `the rst signal generating means H 'generates a basicvsignalfor predetermining .the value .at which the variable is to -be maintained. The means I8' is responsive to the variablefand. generates .a signal Whichvatzthe predetermined .value ,is requal .magnitude ,but-.ropposed .in character .to that .generated by 'the means 11T, `so Vas tonullify both signals, andgis operable with a rise .in .the variable to ygenerate a signallarger than thatjgenerated by themeans l1 Yand with a fall in the variable to` generate a signal smaller .than that of tbemeans H. The

third signal generating means i9 is again in the form of a potentiometer havingga Winding 2U anda movable contact 22. The midpointof the winding 2t' is by a lead 23 represented as electrically connected with the means il', while the movable Contact 22 isby a leadZ .represented .as electrically connected ,With Va .signal conditioning and vamplifying circuit .diagrammatically represented at .25'. Thesignal generatingmeans il' Yand E3' are, ol course, also electrically Vconnected with Ythe circuit 25' and withpne another, with these -connections here represented by the leads Z and v2l".

The movable Contact 22 of the .third signal generating means I9' is still adapted to .be actuated by the differential movement of the valve Il and of a .resetting means, generally designated 3D'. In order that the movable contact 22 may be influenced by adjustment of both the valve H and the resetting means 30', it is operatively coupled to these means through a planetary gear .system generally designated 3i. This means comprises a first driving gear A32' and a second driving gear 3.3. The gear-32' is driven from the shaft I3 while the gear 33 is driven from the resetting means3, as will presently .be described. A third elemente of the planetary gear system is geared in Well known manner to the driving gears to reflect the diiferential Ymovements of those gears, and this element is, through suitable means, represented by a shaft'35, connected tothe movable contact 22'.

The resetting means 353' comprisesarst vdisk 31' driven from a constant speed motor 38 through a Variable transmission 43. The resettingmeans 3B is completed by a second disk 39' and a cylinder 40' fast with the dri-ving gear 33'. As pointed out in greater particularity in connection with Fig. 1, the disk 39 is disposed atright anglesto the disk 31' and .has its-periphery in frictional'engagement with a face of the disk and `with the cylinder 4B'. The` disk 39' is adapted to beshifted radially of the disk A connected to a source of constant potential 41, f

and a movable contact 48. The contact 48 is by a lead 49 connected `to one end of the winding 2D', While the other end of this Winding is by a lead 58 connected through branch leads 5I and 52 to the opposite ends of the winding 46. The branch lead 52 is also connected to the remaining terminal of the voltage source 41. l It will be seen from the foregoing that, Whereas -the signal generated by the means I9' is zero, A-when the contact 22 is in the neutral position shown, and increases in magnitude as the contact moves in either direction from its neutral position (assuming a constant voltage impressed Y on the winding the potentiometer 45, however, impresses a maximum voltage on the winding 20 when the movable contact 48 is in the neutral position shown, and impresses a progressively decreasing voltage as the contact 48 moves in either direction away from its neutral position. The signal generated by the means I9'. therefore, will be dependent not merely upon the position of its movable contact 22' but also upon the position of the contact 48 of the potentiometer 45.

The contact 48 of the potentiometer 45 is moved by means identical with those moving the contact 22. Suiiice it to say, therefore, that there is provided in this form of the invention a second planetary gear systemgenerally designated 55, comprising a first driving gear 56, a second driving gear 51, and an element 58 having a movement indicating the diierential of the movements of the driving gears 56 and 51. The gear 56 is driven from the shaft I3', while the gear 51 is driven by a cylinder 59 forming part of asymptotic means, generally designated 68. This means includes a rst disk 6I driven at a constant rate by the motor 38 through a variable transmission 82. kCompleting the asymptotic means 68 is a disk 63 interposed between the disk 6I and the cylinder 59 and adapted to be shifted radially of the disk 6I with movement of the element 58. Herein the disk 63 is shown rotatable on but held against axial shifting along a shaft 64 which eX- tends from the element 58 to the movable contact 48.

In this form of the invention, greatly enhanced iiexibility of control is obtained. Depending upon the magnitude of the voltage impressed on the winding 20' of the third signal generating means I9', and further depending upon the time when such voltage is impressed, the signal generated by the means I9' may take on a substantially different character. For example, by proper adjustment of the devices a mode of operation can be obtained which is very desirable and, moreover, is one that is commonly sought. More particularly, this mode of operation is one in which the proportional control means, that is, the signal generating means I9', is temporarily either delayed in the generation of a signal, or the application or effect of the signal is delayed so as to permit the signal calling for adjustment of the valve means II' to have full sway for an initial period of time. With the signal generated by the proportional control means thus temporarily Withheld, the valve means I is more rapidly adjusted with the entire system thus rendered more quickly responsive. This mode of operation could be obtained by having the asymptotic means 60 driven at a slow rate and the asymptotic means 30' driven at a high rate. On the other hand, the Various devices might be adjusted to have the lasymptotic means 60 driven at a high rate by the motor-38 and the asymptotic means 30 driven ata very slow rate. Under these conditions, the signal generated by the means I 9 -would remainat a higher magnitude for a longer lperiod of time for the movable contact 48 would be quickly returned to its neutral position to impress the maximum voltage upon the winding 28'. It will be appreciated that in between these two extremes the speeds at which the means 30 and 65 are operated could be varied, with each variation producing a slightly different signal produced by the means I9.

Turning now to the form of the invention shown in Fig. 3, it will be seen that the system is basically the same as that disclosed in Fig. 1 with the exception of the precise effect of the proportional control means. The invention is still disclosed as embodied in a system for maintaining constant a variable, herein the pressure of the fluid in a conduit I This pressure is varied by controlling means taking the form of a valve II" driven in opposite directions and at varying speeds form a reversible, variable speed, electric motor I2" through a shaft I3" and necessary gearing or linkage. Governing the electric motor are a first, a second, and a third electric signal generating means II, I3" and I 9", respectively. Of

these, the first signal generating means l1" generates a basic signal for predetermining the value at which the variable is to be maintained. The means I8" is responsive to the variable and generates a signal which at the predetermined value is equal in magnitude but opposed in character to that generated by the means I1", so as to nullify both signals, and is operable with a rise in the variable to generate a signal larger than that generated by the means I1 and with afallA in the variable to generate a signal smaller than that of the means I1". T'he third signal generating means I9" is again in the form of a potentiometer having a winding 28, a source of potential 2|", and a movable contact 22". The movable contact 22" is by a lead 24 represented as electrically connected with a signal conditioning and amplifying circuit diagrammatically reresented at 25", and the signal generating means I1 and I8" are, of course, also electrically connected with the circuit 25" and with one another, with these .connections here represented by the leads 25 and 21".

The movable contact 22" of the third signal generating means I9 is still adapted to be actuated by the diierential movement of the valve I I" and of a resetting means, generally designated 38". In order that the movable contact 22" may be iniiuenced by adjustment of both the valve I and the resetting means 38", it is operatively coupled to these means through a planetary gear system, generally designated SI". This means comprises a first driving gear 32" and a second driving gear 33". The gear 325' is driven from the shaft I3, while the gear 33" is driven from the resetting means 38, as will presently be described. A third element 34 of the planetary gear system is geared in well known manner to the driving gears to reflect the differential movements of those gears, and this element is, through suitable means represented by a shaft 35",' connected to the movable contact 22".

The resetting means 38" comprises a first disk 31" driven from a constant speed motor 38" throughl a variable transmission 43"'. The resetting means Si!" is completed by a second disk 3e"- and a cylinder 138" fast With the driving gear 33"'. As pointed out in greater particularity in connection Lwith Fig. 1, the disk 39" is disposed at'right angles to the disk 31"' and has its periphery in frictional engagement with a face of the disk and With'thecylinder 4B. TheV disk 32" is= adapted to be shifted radiallyv of the disk 3l" as" the' movable contact 22l is shifted. Herein the disk 39" is shown as mounted on the shaft 35"'.

In this form of the invention, the feed-back signal is not derived entirely from the signal generating'means l 9 but is derived jointly from the means l 9 and a fourth signal generating` means 61. This latter means is also a potentiometer and comprises a Winding' 68, a source of potential 69 and a movable contact 10./ A lead 1I connects the mid-'points of the two windings 2D and 58 while" a lead 12 connects the movable contact lli with the rst signal generating means l1". Thus theY feed-back signal may vary greatly depending upon the relative magnitude and character of they signals generated bythe means I9" and 61. This latter, of course, depends upon the relative position of the movable contacts 22" and 10 and the magnitude of the potential sources 2| and 69.

The contact 'i0 of the potentiometer 61 is moved by means identical With those moving the contact 22". Suiiice it to say, therefore; that there is providedv in this form of the invention a second planetary gear system, generally designated 55", comprising aA rst driving' gear 56, a second driving' gear 51" and an element 58 having a movementindicating the diierential of the movemerits ofv the driving gears 56 and 51". The gear 5B" is driven from the shaft i3" while the gear 5l is driven by a cylinder 59 forming part' of asymptotic means, generally designated E0". This means includes a first disk 6I driven at a constant rate by the motor 38" through a variable transmission 62". Completingr the asy'mptoticv means 6'0" is' a disk 63"l interposed be- 1 tv'veen the disk 6I" and the`V cylinder 59" and adapted to be shifted radially of the disk 6I with movement of the element 58". Herein the disk 63" is shown rotatable on but held against axial shifting along a shaft 64"' which extends from the element 58" to the movable contact 10.

In this form of the' invention, still greater flexibility of control is obtained. Not only may the rates of operation of the asymptotic means 3U" and 60 be varied with the resultant variations in' an inverse feed-back signal obtained in the other forms, but the potentiometers i9 and 61 may be so connected that with proper adjustment of the asymptotic means an aiding rather than an inverse feed-back signal may be obtained. For' example, if voltage source 69 be made larger than 2l" and asymptotic means 60 be made to have a higher rate of operation than means 30, themeans E1 could temporarilybecome dominant thereby adding to the called-forv change in the valve l Due to the higher rate of return of the contact 'Ill to neutral position, the'means El would, after a brief interval, lose its dominant position to means i9" with its inverse feed-back signal. Here again, therefore, a mode of operation could be obtained in which the application or eiect of the signal generated by the proportional control means and normally tending to offset the signal generated by the means responsive to the condition is temporarily delayed so as to permit tliesystem to'operate fora limited period of time at the rate resulting. from the application` off the full main signal to the motor I2". In fact, itis even possible in this form of theA invention to bring about even more rapid adjustment of the valve H" by sovadjusting the speedrof operation of the asymptotic means that an aiding signal is initially added to the signal generated by the means I8". The above is, of course, but one of the advantages of the enhanced flexibility' of control and others will readily' occur'to those skilled in the art.v

We claim as our invention:

1 In a stabilized control system, means for controlling a variable, means including a device responsive to departure of the variable from a predetermined value generating an electrical signal proportionalr toA the degree of departure and of a character indicating the direction of departure calling for adjustment of said controlling means, and a second signal generating means responsive to adjustment of said controlling means operable as an incident to the primary adjusting movement of said controlling means inv adjustment from an oldV to a new position and independently of said first mentioned signal generating means to generate an electrical signal increasing in magnitude and opposed in character to the signal generated by said rst mentioned signal generating means and combined therewith progressively to reduce the rate of adjustment of said controlling means as said controlling'means approaches the end of the primary movement, and means operating in response to adjustment ofA said controlling means for reducing the signal generated by said second signal generating means at an exponential rate. j

2. A system fori controlling a variable comprising means for controlling the variable including means responsive to an electrical signal for adjusting said controlling meansl in opposite directions and at variable rates depending upon the character and magnitude of the electrical signal, a rst signal generating means adjustable to generate a signal predetermining the value at which the variable is to be maintained, av second signal generating means responsiveto departure of the variable from the predetermined value operableto generate a signal calling for adjustment of said controlling means to restore the variable to its predetermined value, a third signal generating means normally in a neutral position in Which it generates a signal. of zero magnitude and operable to generate a signal of increasing magnitude as it is moved in either direction from its neutral position, all of said signal generating means being connected to the signal responsive means to operate the controlling means, said third signal generating means being moved from neutral position by adjustment of said controlling means to generate arsignal of a character opposed to that generated by said second signal generating means, and means brought into operation as an incident to adjustment of said controlling means and influencing said third signal generating means, to restore the second signal generating means to neutral position at an exponential rate.

3. A system for controlling a variable comprising means for controlling the variable including means responsive to an electrical signal for adv justing said controlling means in opposite directions and at variable rates depending upon the character and magnitude of the electrical signal, a rst signal generating means adjustable to generate a signal predetermining the value at which the variable is to be maintained, a second signal generating means responsive to departure of the variable from the predetermined value operable to generate a signal calling for adjustment of said controlling means to restore the variable to its predetermined value, a third signal generating means normally in a neutral position in which it generates a signal of zero magnitude and operable to generate a signal of increasing magnitude as it is moved in either direction from its neutral position, all oi said signal generating means being connected to said signal responsive means to operate the controlling means, asymptoticallyoperating means, and means for actuating saidthird signal generating means driven jointly from said controlling means and said asymptotic means, initial movement of said controlling means acting to move said third signal generating means away from neutral in a direction to generate a signal opposing that generated by said second signal generating means and said asymptotic means being placed in operation as an incident to adjustment of said controlling means and operating to restore said third signal generating means to neutral.

4. A system for controlling a variable comprising means for controlling the variable including means responsive to an electrical signal for adjusting said controlling means in opposite directions and at variable rates depending upon the character and magnitude of the electrical signal, a rst signal generating means adjustable to generate a signal predetermining the value at which the variable is to be maintained, a second signal generating means responsive to departure of the variable from the predetermined value operable to generate a signal calling for adjustment of said controlling means to restore the variable to its predetermined value, a third signal generating means normally in a neutral position in which it generates `a, signal of zero magnitude and operable to generate a signal of increasing magnitude as it is moved in either direction from its neutral position, all of said signal generating y means being connected to said signal responsive Ameans to operate the controlling means, asymptotically operating means, said asymptotic means being adjustable to operate on diierent exponential curves, and means for actuating said .third signal generating means driven jointly from said controlling means and said asymptotic means, initial'movement of said controlling means acting to move said third signal generating means away from neutral-in a direction to generate a signal opposing that generated by said second signal generating means and said asymptotic means being placed in operation as an incident to adjustment of said controlling means and operating to restore said third signal generating means to neutral.

5. A system for controlling a variable comprising means for controlling the variable including means responsive to an electrical signal foradiable to its predetermined value, a third signal andsaid controlling means governing generating means normally in a neutral position in which it generates'a signal of zero magnitude and operable to generate a signal of increasing magnitude as it is moved in either direction from its neutral position, all of said signal generating means being connected to said signal responsive means to operate the controlling means, asymptotically operating means, and planetary gear means for actuating said third signal generating means driven jointly from said controlling means and said asymptotic means, initial adjustment of said controlling means tending to move said third signal generating means from neutral position in a direction causing generation of a signal opposing that generated by said second signal generating means and rendering said asymptotic means operative, said asymptotic means tending to restore said third signal generating means to neutral position.

6. In a stabilized control system, means for controlling a variable, means responsive to departure of the variable from a predetermined value to generate a signal calling for adjustment of said controlling means, power means controlled by the signal for adjusting said controlling means, feed-back signal generating means placed into operation as an incident to adjustment of said controlling means, asymptotic means for controlling said feed-back signal means jointly with said controlling means, and means exercising additional control over said feed-back means including a second means placed in operation as an incident to adjustment of said controlling means and functioning at an exponentially decreasing rate.

7. A system for controlling a variable comprising means for controlling the variable inoluding means responsive to an electrical signal for adjusting said controlling means in opposite directions and at variable rates depending upon the character and magnitude of the electrical signal,a rst signal generating means adjustable to generate a signal predetermining the value at which the variable is to be maintained, a second signal generating means responsive to departure of the variable from the predetermined value operable to generate a signal calling for'adjustment of said controlling means to restore the variable to its predetermined value, a third signal generating means normally in a neutral position in which it generates a signal of zero magnitude and operable to generate a signal of increasing magnitude as it is moved in either direction from its neutral position, a first asymptotically operating means, diierential means for moving said third signal generating means jointly actuated by said controlling means and said asymptotic means to cause said third signal generating means to generate a signal opposing that generated by the second signal generating means, and means providing the potential for said third signal generating means including a second asymptotically operating means and differential means jointly actuated `by said second asymptotic means said potential providing means.

8. A system for controlling a variablecomprising means for controlling the variable including means responsive to an electrical signal for adjusting said controlling means in opposite Adirections and at variable rates depending upon the character and magnitude of the electrical signal, a rst signal generating means adjustable to generate a signal predetermining the'value at which the variable-is to be maintained, a second signal generating vmeans .responsive fto departure fofthe variable Afrom the predetermined value operable to generate a .signal calling vfor adjustment of said controlling means to restore the variable to its predetermined value, a rstpotenttio-meter'forminga third signal generating means and connected in `feed-back relation -with said iii-'st and lsecond signal generating means, a second potentiometer constituting the voltage 'source of 'said first potentiometer, a diierential means for adjusting each of said potentiometers actuated from said controlling means, and .an 'asymptotically operatingmeans also driving each diierential means, the voltages of said potentiometers for like .adjustments varying in opposite directions.

`9. A system for controlling a variable comprisying means for controlling the variable including means responsive to an electrical signal for adjusting said controlling means `in opposite directions and at variable .rates depending upon the character and magnitude of the electrical signal,

a first signal generating means adjustable to generate ka signal predetermining the value at which the'variable is to be maintained, a second signal generating means responsive to departure of the variable from the predetermined value voperable to generate a signal calling for adjustment' of said controlling means to restore the variable to its predetermined value, arst potentiometer forming a third signal generating means connected in feed-back relation with said rst .and second signal generating lmeans and includnrst potentiometer and including a movable contact, said second potentiometer operating upon movement of its movable contact in either direcltionfa-Way from a neutral position to decrease the voltage applied to said first potentiometer, a differential means for adjusting each or" said movable contacts actuated from said controlling means, and an asymptotically operating means also driving each differential means, said asymptotically operating means being rendered operative as an incident to movement of the associated movable contact away from neutral position and tending to actuate said diierential means to restore the movable Vcontact to neutral position.

10.4A system for controlling a variable comprising means for controlling the variable including Vmeans responsive to an electrical signal vfor adjusting said controlling means in opposite directions and at variable rates depending upon the vcharacter and magnitude of the electrical signal, a rst signal generating means adjustable to generate a signal predetermining the value at which the variable is to be maintained, a second signal generating means responsive to departure of the yvariable from the predetermined value operable -to generate a signal calling for adjustmentofvsaid controllingr means to restore the variable to its predetermined value, a nrst potentiometer forming a third signal generating means .connected in feed-back relation With said rst yand second signal generating means and including a movable contact and operable With a xed potential source to generatea signal of increasyingmagniture as the contact is moved in either direction from a neutral position, a second potentiometer constituting the voltage source of said first potentiometer and including a movable conescasos tact, said second potentiometer operating Aupon movement of .its :movable contact in either direc- -driven from the differential movements of fsaid driving gears, one of said driving gears of each planetary gear system being driven from .said controlling means, an asymptotically loperating means lassociated with each -planetary .gear sy-stem including a constantly rotating disk and means fortransmitting rotation of the disk tothe other of said driving gears including aseconddisk disposed at right angles to the rst mentioned disk and having frictional engagement withD a surface of said rst mentioned disk, and means operatively connecting the third element of each planetary gear system with the second disk -of the associated asymptotically operating means and with the movable contact of one of said potentiometers in such manner that the second disk receives no rotation from the nrst mentioned .disk when the movable contact is in neutral position.

11. In a stabilized control system, means for controlling a variable, means responsive to `departure of the variable from a predetermined value 'to generate a signal calling for adjustment of said controlling means, means responsive toV the signal for `adjusting said controlling means, and means responsive to vadjustment of `said controlling means operable to generate a feed-back signal, and a second means responsive to adjustment of said controlling means and including-a potentiometer controlling the feed-back signal generating means to generate a signal which initially aids and subsequently counteracts the signal calling for adjustment of said controlling Illel'ls.

12. In a stabilized control system, meansfor controlling a variable, means responsive to departure of the variable from a predetermined value to generate a signal calling for adjustment of said controlling means, means vresponsive to the signal adjusting said controlling means, means responsive to adjustment of said controlling means operable togenerate a feed-back signal, said last mentioned means comprising a pair of signal generating devices connected to have the signal of the one modified by the signal of the other, and drive means for each signal generating device rendered operative as an incident to adjustment of said last named signal generating means from a neutral position and functioning to tend to return said last named signal generating means to neutral position, said drive means beingA adjustable to operate `at various rates.

13. In a stabilized control system, means for controlling a variable, means responsive to departure of the variable from a predetermined value to generate a signal calling for adjustment of said controlling means, means responsive to the signal adjusting said controlling means, means for generating a feed-back signal including a pair of signal generating devices connected together so that the signal of the one modifies the signal of the other, each of said devices having a neutral position in which no signal is generated, and means for adjusting each of said signal generating devices comprising a planetary gear system and asymptotically operating means, the planetary gear system being driven by said controlling means and said asymptotically operating means and having an element actuated by the differential drive imparted to the planetary gear system operatively associated with the signal generating device and an element of said asymptotically operating means whereby adjustment of said controlling means tends to move the signal generating means away from neutral position and tends to render operative said asymptotically operating means while said asymptotically operating means tends to restore the signal generating means to neutral position.

14. In a stabilized control system, means for controlling a variable, a first signal generating means operable to generate a signal indicating the value at which the variable is to be maintained, a second electrical signal generating means responsive to departure of the variable from the predetermined value operable to generate a signal calling for adjustment of said controlling means, means responsive to the resultant signal for adjusting said controlling means and said feed-back signal generating means comprising a third and a. fourth signal generating means connected in series and having a normal adjustment in which no signal is generated, and means for each said third and fourth signal generating means for effecting adjustment thereof comprising a planetary gear system having one driving gear driven as an incident to adjustment of said controlling means and a second driving gear and asymptotically operating means driving said second driving gear, and an element actuated by the differential movements of said driving gears operatively associated with one of said third or fourth signal generating means and with an element of said asymptotically operating means, said controlling means tending to adjust the signal generating means associated therewith away from neutral position and said asymptotically operaing means tending to restore the associated signal generating means to neutral position.

15. In a stabilized control system, a first signal generating means responsive to departure of a variable from a predetermined value to generate a signal indicative of the direction of departure 18 and proportional to the extent of departure, mechanism for controlling the variable, a second signal generating means connected to have its signal combined with that of said first signal generating means, means responsive to the combined signal governing said mechanism for controlling the variable, differential means having a rst driving element connected to be driven in a straight line relationship to said mechanism for controlling the Variable, and a differentially operated element, said second signal generating means being connected to said diierentially operated element to be influenced by adjustment of said mechanism for controlling the variable and operable in the absence of other influencesv to generate a signal opposed in character to that generated by said rst signal generating means and increasing as said mechanism for controlling the variable is initially adjusted from an old to a new position, and means connected to a second driving element of said differential means also influencing said second signal generating means to restore the same to normal position, said last named means coming into operation as an incident to any adjustment of said mechanism for controlling the variable and operating at an exponential rate.

HERBERT ZIEBOLZ. PAUL GLASS.

REFEREN CES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,278,396 Saur Mar. 31, 1942 2,335,163 Smith Nov. 23, 1943 y2,367,746 Williams Jan. 23, 1945 2,376,513 Shaffer May 22, 1945 2,405,774 Blakeslee Aug. 13, 1946 FOREIGN PATENTS Number Country Date 350,995 Great Britain June 11. 1931 

